System and method docketing a robotic mower

ABSTRACT

A method and a system for docketing a robotic mower with a charging station. The system includes a boundary wire and a charging station loop wherein the boundary wire makes a loop in the charging station that is narrower than and crosses the charging station loop. A return signal is received from a control unit commanding the robotic mower to return to the charging station. The robotic mower is controlled to follow the boundary wire until the charging station loop is detected. The robotic mower then follows the charging station loop until a crossing between the charging station loop and the boundary wire loop is detected. The robotic mower is controlled to follow the charging station loop a first distance, and then continuing to drive the robotic mower in a direction straight forward for a second distance. When the robotic mower has moved the second distance it is turned a predefined angle towards the charging station and controlled to follow the boundary wire loop until a charging position is reached.

TECHNICAL FIELD

The present invention relates generally to a system and method forreturning a robotic mower back to a charging station when a battery ofthe robotic mower needs to be recharged, and more specifically fordocketing the robotic mower with a charging station.

BACKGROUND ART

Robotic mowers, also called self-propelled lawnmowers, are generallyknown. These robotic mowers are provided with a rechargeable battery.When the remaining power in the battery is below a certain level therobotic mower is programmed to return to the charging station torecharge the battery. In prior art, there are many different methods forreturning the robotic mower to the charging station. One common methodis that the robotic mower, when receiving a command to return to thecharging station, continues its movement until a boundary wire isdetected and then follows the boundary wire to the charging station thatis provided somewhere along the boundary wire. When the robotic mower isclose to the charging station a docketing process is started such thatthe robotic mower is safely guided into contact with a chargingconnector of the charging station.

U.S. Pat. No. 8,433,468 discloses a robotic mower home finding system,in which a charging station is connected to an outer boundary wire loop.The robotic mower comprises a plurality of sensors for correlating thedistance of each sensor to the outer boundary loop. When the roboticmower is commanded to return to the charging station it continues itsmovement until the plurality of sensors find the outer boundary wireloop and then follows the outer boundary wire loop along a path that isoffset a specified distance parallel to the outer boundary wire loop.When an inner wire loop, connected to the charging station, is detectedby the plurality of sensors the robotic mower is turned perpendicular tothe outer boundary wire loop in order to enter the charging station. Thespecified distance is changed each time the robotic mower returns hometo the charging station. By varying the specific distance, damage to theturf along the boundary wire is avoided, since the robotic mower followsdifferent paths back to the charging station.

U.S. Pat. No. 8,942,862 discloses a method for guiding a robotic gardentool to a predetermined position, i.e. to a charging station. Therobotic garden tool comprises a control unit and a sensor unit forwirelessly detecting guiding signals. The guiding signals are generatedin guide wires which the robotic garden follows when it returns back tothe charging station. Using guide wires often enables a shorter andfaster way back to the charging station compared to following a boundarywire. When a first guiding signal is detected from a first guide wire,the robotic garden tool follows the first guiding signal at a variabledistance from the first guide wire towards the charging station inresponse to a command from the control unit. When a second guidingsignal is detected from a second guide wire the robotic garden followsone of the first or the second guiding signal at a pre-configureddistance from the corresponding guide wire towards the charging station.The second guiding signal is detected within a predetermined distancefrom the charging station.

Thus, there are described numerus different ways in prior art to returna robotic mower to a charging station. However, there is still room forimprovements and especially for the final stage, i.e. the docketing tothe charging station. The problem with the docketing process is to makean accurate line up of the robotic mower that ensures that the chargingcontacts of the robotic mower will securely attach to the docketingstation.

SUMMARY OF INVENTION

An object of the present invention is to provide a method for returninga robotic mower to a charging station when the robotic mower needs to berecharged and where the docketing process, i.e. the process when therobotic mower is about to dock with charging contacts in the chargingstation, is simple and reliable.

According to one aspect of the present invention this object is achievedby a method for docketing a robotic mower with a charging station, whichmethod is performed by a system comprising the robotic mower having acontrol unit and at least one sensor, a boundary wire, a chargingstation loop and the charging station and wherein the boundary wiremakes a loop in the charging station that is narrower than and crossesthe charging station loop. The method comprises receiving a returnsignal from the control unit that the robotic mower shall return to thecharging station. In response thereto, the robotic mower is controlledto follow the boundary wire at a distance until the charging stationloop is detected by means of the at least one sensor. The robotic moweris then controlled to follow the charging station loop in a directionaway from the boundary wire, by using at least one sensor, until acrossing between the charging station loop and the boundary wire loop isdetected, by means of the at least one sensor. Thereafter, the roboticmower is controlled to follow the charging station loop a first distanceafter detection of the crossing, and then continuing to drive therobotic mower in a direction straight forward for a second distance.When the robotic mower has moved the second distance it is turnedtowards the charging station, by means of the control unit, and then therobotic mower is controlled to follow the boundary wire loop with atleast one sensor until a charging position is reached.

In an exemplary embodiment, the robotic mower is controlled to followthe boundary wire at a random distance.

In another exemplary embodiment, the robotic mower reaches the firstdistance and second distance when at least one sensor is in a knownposition in front of the charging station. The first and second distanceare predetermined distances.

In an exemplary embodiment, the robotic mower turns towards the chargingstation until at least one sensor passes the boundary wire loop.

In another exemplary embodiment the robotic mower is provided with threesensors, two front sensors and one rear sensor and the detection of thecharging station loop is determined when one of the two front sensorspasses the charging station loop.

In yet another exemplary embodiment the robotic mower is provided withfour sensors, two front sensors and two rear sensors and the firstdistance and the second distance are reached when one of the two rearsensors reaches the charging station loop and the boundary wire loop,respectively.

Another object of the present invention is to provide a system fordocketing a robotic mower with a charging station when the robotic mowerneeds to be recharged and where the docketing process, i.e. the processwhen the robotic mower is about to dock with charging contacts in thecharging station, is simple and reliable.

According to another aspect of the present invention this object isachieved by a system for docketing a robotic mower with a chargingstation, comprising the robotic mower, a boundary wire, a chargingstation loop and the charging station and wherein the boundary wiremakes a loop in the charging station that is narrower than and crossesthe charging station loop, the robotic mower further comprises a controlunit and at least one sensor, wherein the control unit comprises aprocessor and a memory, the memory comprising instructions which whenexecuted by the processer causes the system to:

receive a return signal from the control unit that the robotic mowershall return to the charging station,control the robotic mower to follow the boundary wire at a distance,detect the charging station loop by means of the at least one sensor,control the robotic mower to follow the charging station loop, in adirection away from the boundary wire, with at least one sensor,detect, by means of the at least one sensor, a crossing between thecharging station loop and the boundary wire loop,control the robotic mower to follow the charging station loop a firstdistance after detection of the crossing,continue to drive the robotic mower in a direction straight forward fora second distance,turn, by means of the control unit, the robotic mower towards thecharging station, andcontrol the robotic mower to follow the boundary wire loop with at leastone sensor until a charging position is reached.

In an exemplary embodiment, the robotic mower of the system is furthercaused to follow the boundary wire at a random distance.

In another exemplary embodiment, the robotic mower of the system isfurther caused to determine that the first distance and second distanceare reached when at least one sensor is in a known position in front ofthe charging station. The first and second distance are predetermineddistances.

In an exemplary embodiment, the robotic mower of the system is caused toturn towards the charging station until at least one sensor passes theboundary wire loop

In another exemplary embodiment, the robotic mower is provided withthree sensors, two front sensors and one rear sensor and the system isfurther caused to determine detection of the charging station loop isdetermined when one of the two front sensors passes the charging stationloop.

In yet another exemplary embodiment, the robotic mower is provided withfour sensors, two front sensors and two rear sensors and wherein thefirst distance and the second distance are reached when one of the tworear sensors reaches the charging station loop and the boundary wireloop, respectively.

In yet another exemplary embodiment, the system is further caused to useboth front sensors to control the robotic mower, such that the roboticmower follows the boundary wire loop to the charging position.

Another object of the present invention is to provide a method, that issimple and reliable, for docketing a robotic mower with a chargingstation when the robotic mower needs to be recharged and the roboticmower uses a guide wire when returning back to the charging station.

According to yet another aspect of the present invention this object isachieved by a method performed by a system for docketing a robotic mowerwith a charging station, wherein the system comprises the robotic mowerhaving a control unit and at least one sensor, a boundary wire, acharging station loop, the charging station and at least one guide wire.The boundary wire makes a loop in the charging station that is narrowerthan and crosses the charging station loop. The method comprisesreceiving a return signal from the control unit that the robotic mowershall return to the charging station. In response thereto, the roboticmower is controlled to follow the guide wire at a random distance untilthe robotic mower detects the charging station loop by means of the atleast one sensor. When the charging station loop is detected, therobotic mower is controlled to move closer to the guide wire until it isdetected, by means of the at least one sensor, that the robotic mowerpasses the boundary wire loop. The robotic mower is the controlled tofollow the boundary wire loop with at least one sensor until a chargingposition is reached.

In an exemplary embodiment, the robotic mower is provided with threesensors, two front sensors and one rear sensor and the detection of theboundary wire loop is determined when one of the front sensors passesthe charging station loop. In another exemplary embodiment, both frontsensors are then used to control the robotic mower during the docketingprocess, such that the robotic mower follows the boundary wire loop tothe charging position.

Another object of the present invention is to provide a system that issimple and reliable and used for docketing a robotic mower with acharging station when the robotic mower needs to be recharged and therobotic mower uses a guide wire when returning back to the chargingstation.

According to another aspect of the present invention this object isachieved by a system for docketing a robotic mower with a chargingstation, the system comprises the robotic mower, a boundary wire, atleast one guide wire, a charging station loop and the charging station.The boundary wire makes a loop in the charging station that is narrowerthan and crosses the charging station loop. The robotic mower comprisesa control unit and at least one sensor, wherein the control unitcomprises a processor and a memory, the memory comprising instructionswhich when executed by the processer causes the system to:

receive a return signal from the control unit that the robotic mowershall return to the charging station,control the robotic mower to follow the guide wire at a random distance,detect the charging station loop by means of the at least one sensor,control the robotic mower to move closer to the guide wire,detect, by means of the at least one sensor, that the robotic mowerpasses the boundary wire loop, andcontrol the robotic mower to follow the boundary wire loop with at leastone sensor until a charging position is reached.

In an exemplary embodiment, the robotic mower is provided with threesensors, two front sensors and one rear sensor and the system is furthercaused to determine detection of the charging station loop when one ofthe front sensors passes the charging station loop. In another exemplaryembodiment, the system is further caused to use both front sensors tocontrol the robotic mower during the docketing process, such that therobotic mower follows the boundary wire loop to the charging position.

According to one aspect there is achieved a computer program comprisingcomputer program code, which computer program code is adapted, ifexecuted by the processer of the control unit, to implement the methodsdescribed above.

By providing a method and a system for docketing a robotic mower with acharging station according to the present invention it is possible toachieve a reliable yet simple docketing process, where the robotic moweris safely guided into contact with the charging contacts of the chargingstation.

The solution will also reduce the component costs for a charging stationcompared to having separate loop wires for guiding the mower to acharging position. The reduced number of loop wires will also reduce thenumber unique codes that are needed and used by the system which furtherreduces the complexity.

BRIEF DESCRIPTION OF DRAWINGS

The invention is now described, by way of example, with reference to theaccompanying drawings, in which:

FIG. 1 a schematic view of a robotic mower system.

FIG. 2a is a schematic view of an exemplary embodiment of the roboticmower.

FIG. 2b is a schematic view of another exemplary embodiment of therobotic mower.

FIG. 3 is a schematic block diagram of a control unit in the roboticmower.

FIG. 4 is a schematic block diagram of a signal generator.

FIG. 5a to FIG. 5i show different docketing steps when the robotic mowerdocks with a charging station via a boundary wire.

FIG. 6a to FIG. 6d show different docketing steps when the robotic mowerdocks with a charging station via a guide wire.

FIG. 7 is a flow chart of an exemplary method for docketing the roboticmower with the charging station.

FIG. 8 is a flow chart of another exemplary method for docketing therobotic mower with the charging station.

DESCRIPTION OF EMBODIMENTS

In the following, a detailed description of exemplary embodiments fordocketing a robotic mower with a charging station according to thepresent invention will be presented.

FIG. 1 shows a schematic overview of a system for performing the methodof docketing a robotic mower 2 with a charging station 11. The roboticmower 2, or as it also may be called a self-propelling lawnmower, isbattery powered and needs to be recharged at regular intervals. Therobotic mower 2 is during operation configured to move across an area Asurrounded by a boundary wire 4. As is obvious the robotic mower 2 isdepicted somewhat enlarged for the sake of clarity. The boundary wire 4may be configured in many different ways, such that it delimits the areaA within which the robotic mower 2 is allowed to move. The boundary wire4 is preferably provided under the ground in the lawn, such that is notvisible, but may also be provide on or above the ground. The boundarywire 4 could be an ordinary copper wire of single-core type. There areof course also other options, which are well-known by a person skilledin the art, such as multi stranded wire types. As may be seen in FIG. 1the boundary wire 4 makes a loop 4 a in the charging station 11. Thisloop 4 a will be used to guide the robotic mower 2 into charging contactwith the charging station 11, which will be described further below.

The system also comprises the charging station 11 mentioned above. Thecharging station 11 is shown with dotted lines in FIG. 1 in order to notunnecessary smudge the figure. The charging station itself 11 may beseen as the place where the charging of the robotic mower 2 takes place,but could for an example also be provided with a charging plate ontowhich the robotic mower 2 is guided when performing docketing. Acharging plate will make the docketing process more precise, since therobotic mower 2 will be at an even and predictable ground during thedocketing process. In order to identify where the charging station 11 islocated, there is provided a charging station loop 10 around thecharging station 11. As shown in FIG. 1 the boundary wire loop 4 a isnarrower than and crosses the charging station loop 10.

A system according to the present invention may also as an optioncomprise one or more guide wires 8. A guide wire 8 is a wire that therobotic mower 2 may follow when returning to the charging station 11.Normally the robotic mower follows the boundary wire 4 back to thecharging station 11, which depending on where the robotic mower 2 startsto follow the boundary wire 4 may be quite a distance. By using a guidewire 8 it is possible to return the robotic mower 2 to the chargingstation 11 in a faster and less energy consuming way, which is wellknown in the art.

The boundary wire 4, the charging station loop 10 and the optional oneor more guide wires 8 are all connected to a signal generator 6 whichfeeds each wire and loop with an Alternating Current, AC, signal, suchthat the robotic mower 2 may recognize which wire or loop it isdetecting when it is within sensing distance, which is also known in theart.

Turning now to FIG. 2a , an exemplary embodiment of the robotic mower 2will be closer described. The robotic mower 2 comprises a control unit22, wheels 20, at least one sensor 12, 14 and/or 16 and a battery 18.The control unit 22, which will be closer described in conjunction withFIG. 3, comprises among other things a processor 80 for controlling themovement of the robotic mower 2. When the robotic mower 2 is inoperation the sensors 12, 14 and 16 sense the magnetic field that isgenerated in the boundary wire 4, the charging station loop 10 and whereappropriate also the one or several guide wires 8. The sensed magneticfield (signal) is decoded in the control unit 22 to determine from whichloop or wire it was received. In a preferred embodiment, the roboticmower 2 is provided with three sensors, two front sensors 12, 14 and onerear sensor 16. In this embodiment one of the two front sensors 12, 14may be used to detect the presence of the charging station loop 10. Thisconfiguration may be beneficial for increasing the precision in thedocketing process.

FIG. 2b shows another embodiment of the robotic mower 2, the differenceto the previous embodiment being that it comprises two rear sensors 17,19 instead of one. The rest of the description of the robotic mower 2will therefore not be repeated here. With two rear sensors 17, 19 theprecision of the docketing process may be further enhanced. One or bothof the rear sensors 17, 19 may for example be used when determining thata first distance and second distance has been reached in relation to thecharging station loop 10 and the boundary wire loop 4 a, respectively,during the docketing process as will be further be described below.

With reference to FIG. 3, the control unit 22 of the robotic mower 2will be closer described. The control unit 22 comprises, as mentionedabove the processor 80 and a memory 82. The memory 82 may comprise acomputer program 84 comprising computer program code, i.e. instructions.The computer program code is adapted to implement the method stepsperformed by the robotic mower 2 when the code is executed on theprocessor 80. The control unit 22 further comprises an interface 86 forcommunication with the sensors 12, 14 and 16, and the sensors 12, 14, 17and 19, respectively, and a motor that operates the robotic mower 2.

The processor 80 may comprise a single Central Processing Unit (CPU), orcould comprise two or more processing units. For example, the processor80 may include general purpose microprocessors, instruction setprocessors and/or related chips sets and/or special purposemicroprocessors such as Application Specific Integrated Circuits(ASICs), Field Programmable Gate Arrays (FPGAs) or Complex ProgrammableLogic Devices (CPLDs). The processor 80 may also comprise a storage forcaching purposes.

FIG. 4 depicts the signal generator 6, which also comprises a processor60 and a memory 62. The memory 62 may comprise a computer program 64comprising computer program code, i.e. instructions. The computerprogram code is adapted to implement the method steps performed by thesignal generator 6 when the code is executed on the processor 60. Thesignal generator 6 further comprises an interface 66 for transmittingthe generated AC signal to the boundary wire 4, charging station loop 10and if appropriate the guide wire or wires 8.

As for processor 80 also the processor 60 may comprise a single CentralProcessing Unit (CPU), or could comprise two or more processing units.For example, the processor 60 may include general purposemicroprocessors, instruction set processors and/or related chips setsand/or special purpose microprocessors such as Application SpecificIntegrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs) orComplex Programmable Logic Devices (CPLDs). The processor 60 may alsocomprise a storage for caching purposes.

Turning now to FIG. 5a to FIG. 5i and FIG. 7 exemplary embodiments ofthe method according the present invention will be closer described. Themethod starts in step S100 in which the robotic mower 2 receives areturn signal from the control unit 22, which commands the robotic mower2 to return to the charging station 11. Step S100 may be triggered bydetecting that the power in the battery 18 is lower than a predeterminedlimit. The predetermined limit is set such that the robotic mower 2 maysafely return to the charging station 11 before the battery 18 is empty,even if it happens to be the longest possible way back to the chargingstation 11.

When the robotic mower 2 has received the command to return to thecharging station 11, it commences with mowing the area A until itdetects the boundary wire 4 by means of one or more of the roboticmower's 2 sensors 12, 14 and 16 or 12, 14, 17 and 19, respectively. Whenthe boundary wire 4 has been detected, the robotic mower 2 iscontrolled, in step S102, to follow the boundary wire 4 at a fixed orrandom distance R_(d). The randomness may be determined by a randomgenerator in the control unit 22 each time that the command to returnthe robotic mower 2 to the charging station 11 is generated. Thus, thecontrol unit 22 determines that it is time to return to the chargingstation 11, generates a random distance and sends a command to therobotic mower 2 to return and which distance to the boundary wire 4 touse when returning. By using different distances when the robotic mower2 is to return to the charging station 11 tracking in the lawn may beavoided.

The robotic mower 2 will follow the boundary wire 4 at the randomdistance R_(d) until detecting, in step S104, the charging station loop10 by means of at least one of the sensors 12, 14, 16, 17 or 19. In oneembodiment the detection of the charging station loop 10 is determinedwhen one of the front sensors 12, 14 passes the charging station loop10. As a response thereto, the robotic mower 2 is controlled, in stepS106, by the control unit 22 to follow the charging station loop 10, ina direction away from the boundary wire 4, by using at least one sensor12, 14, 16, 17, 19. In one exemplary embodiment the robotic mower 2 iscontrolled, in step S105 to move in a direction closer to the boundarywire 4 after detecting the charging station loop 10, such that thedocketing process may be better controlled. This is however optional, asis indicated by the dotted lines in FIG. 7.

The robotic mower 2 will follow the charging station loop 10, includingmaking a 90 degree turn as the charging station loop 10 turns 90degrees, until a crossing between the charging station loop 10 and theboundary wire loop 4 a is detected, in step S108, by means of the atleast one sensor 12, 14, 16. The detection of the crossing triggers therobotic mower 2 to follow the charging station loop 10, in step S110, afirst predetermined distance after the detection of the crossing. Thisfirst predetermined distance is long enough to straighten up the roboticmower 2 such that it runs parallel with the charging station loop 10.When the robotic mower 2 has moved the first predetermined distance itcontinues, in step S112, to drive the robotic mower 2 in a directionstraight forward for a second predetermined distance. After this stepS112 the robotic mower 2 is in a position that always will be the sameand that will ensure that the docketing between the robotic mower 2 andthe charging contacts in the charging station 11 will run smoothly.

Thus, in this position the robotic mower will 2 be rotated or turned apredefined angle towards the charging station 11, in step S114, by meansof the control unit 22. The robotic mower 2 may also be turned until thefront sensors 12, 14 pass the boundary wire 4 towards the chargingstation 11. After the turn, the robotic mower 2 is controlled, in stepS116, to follow the boundary wire loop 4 a with at least one sensor 12,14, 16, until a charging position is reached. In an exemplaryembodiment, the robotic mower 2 is provided with three sensors, twofront sensors 12, 14 and one rear sensor 16 and the detection of thecharging station loop 10 is then determined when one of the two frontsensors 12, 14 passes the charging station loop 10. As is understood bya person skilled in the art there are many ways to use three or foursensors in order to guide the robotic mower 2 during the docketingprocess. For example, both front sensors 12, 14 may be used to controlthe robotic mower 2, in step S116, to increase the accuracy when therobotic mower 2 follows the boundary wire loop 4 a to the chargingposition. Furthermore, the width of the boundary wire loop 4 a, may beadapted to the actual distance between the two front sensors 12, 14,which will increase the robustness of the docketing process.

If the robotic mower 2 is provided with four sensors 12, 14, 17, 19instead steps S110 and S112 may be performed in a different way. In stepS110 the first distance is then reached when one of the rear sensors 17,19 is at a known position in front of the charging station 11, forexample when one of the rear sensors 17, 19 reaches the charging stationloop 10. In step S112 the second distance is then reached when one ofthe rear sensors 17, 19 is at a known position in front of the chargingstation, for example when one of the rear sensors 17, 19 reaches theboundary wire loop 4 a. These alternative steps are shown in FIGS. 5hand 5 i.

Turning now to FIG. 6a to FIG. 6d and FIG. 8 another exemplaryembodiment of the method according to the present invention will becloser described. The difference between the previous described methodand this method is that the later one uses a guide wire 8 to return tocharging station 11 instead of boundary wire, which enables a shorterreturn time for the robotic mower 2 when it returns to the chargingstation 11. The method starts in step S200 in which the robotic mower 2receives a return signal from the control unit 22, which commands therobotic mower 2 to return to the charging station 11. As mentioned abovethe return signal may be triggered by detecting that the power in thebattery 18 is lower than a predetermined limit. However, there may alsobe other trigger events, such as a rain sensor that has detected rain.

When the robotic mower 2 has received the command to return to thecharging station 11, it commences with mowing the area A until itdetects the guide wire 8 by means of one or more of the robotic mower's2 sensors 12, 14 and 16. When the guide wire 8 has been detected, therobotic mower 2 is controlled, in step S202, to follow the guide wire 4at a random distance Rd. As mentioned above, the randomness may bedetermined by a random generator in the control unit 22.

The robotic mower 2 will follow the guide wire 8 at the random distanceRd until detecting, in step S204, the charging station loop 10 by meansof at least one of the sensors 12, 14, 16. In one embodiment thedetection of the charging station loop 10 is determined when one of thefront sensors 12, 14 passes the charging station loop 10. As a responsethereto, the robotic mower 2 is controlled, in step S206, by the controlunit 22, to move closer to the guide wire 8. This is done to ensure thatthe robotic mower 2 will cross the boundary wire loop 4 a, whencontinuing to follow the guide wire 8. Thus, how close to the guide wire8 the robotic mower 2 has to be moved is decided by the width of theboundary wire loop 4 a.

The robotic mower 2 continues to follow the guide wire 8 at a closerdistance until it is detected by means of the at least one sensor 12,14, 16, in step S208, that the robotic mower 2 passes the boundary wireloop 4 a. Thereafter, the robotic mower 2 is controlled, in step 210, tofollow the boundary wire loop 4 a with at least one sensor 12, 14, 16until a charging position is reached.

As mentioned above, there are many ways to use three sensors 12, 14 and16 in order to guide the robotic mower 2 during the docketing process.For example, both front sensors 12, 14 may be used to control therobotic mower 2, in step S210, to increase the accuracy when the roboticmower 2 follows the boundary wire loop 4 a to the charging position.Furthermore, the width of the boundary wire loop 4 a, may also in thisexemplary embodiment be adapted to the actual distance between the twofront sensors 12, 14, which will increase the robustness of thedocketing

Although, the present invention has been described above with referenceto specific embodiments, it is not intended to be limited to thespecific form set forth herein. Rather, the invention is limited only bythe accompanying claims.

In the claims, the term “comprises/comprising” does not exclude thepresence of other elements or steps. Furthermore, although individuallylisted, a plurality of means or elements may be implemented by e.g. asingle unit or processor. Additionally, although individual features maybe included in different claims, these may possibly advantageously becombined, and the inclusion in different claims does not imply that acombination of features is not feasible and/or advantageous. Inaddition, singular references do not exclude a plurality. The terms “a”,“an”, “first”, “second” etc. do not preclude a plurality. Referencesigns in the claims are provided merely as a clarifying example andshall not be construed as limiting the scope of the claims in any way.

1-21. (canceled)
 22. A method performed by a system for docketing arobotic mower with a charging station, the system comprising the roboticmower having a control unit and at least one sensor, a boundary wire, acharging station loop and the charging station and wherein the boundarywire makes a loop in the charging station that is narrower than andcrosses the charging station loop, the method comprising: receiving areturn signal from the control unit that the robotic mower shall returnto the charging station, controlling the robotic mower to follow theboundary wire at a distance, detecting the charging station loop bymeans of the at least one sensor, controlling the robotic mower tofollow the charging station loop, in a direction away from the boundarywire, by using at least one sensor, detecting, by means of the at leastone sensor, a crossing between the charging station loop and theboundary wire loop, controlling the robotic mower to follow the chargingstation loop a first distance after detection of the crossing,continuing to drive the robotic mower in a direction straight forwardfor a second distance, turning, by means of the control unit, therobotic mower towards the charging station, and controlling the roboticmower to follow the boundary wire loop with at least one sensor until acharging position is reached.
 23. The method according to claim 22,wherein the robotic mower follows the boundary wire at a randomdistance.
 24. The method according to claim 22, wherein the firstdistance and the second distance are reached when at least one sensor isin a known position in front of the charging station.
 25. The methodaccording to claim 22, wherein the first distance and the seconddistance are predetermined distances.
 26. The method according to claim22, wherein the robotic mower turns towards the charging station untilat least one sensor passes the boundary wire loop.
 27. The methodaccording to claim 22, wherein the robotic mower is provided with twofront sensors and one rear sensor and wherein the detection of thecharging station loop is determined when one of the front sensors passesthe charging station loop.
 28. The method according to claim 22, whereinthe robotic mower is provided with two front sensors and two rearsensors and wherein the first distance and the second distance arereached when one of the two rear sensors reaches the charging stationloop and the boundary wire loop, respectively.
 29. A system fordocketing a robotic mower with a charging station, comprising therobotic mower, a boundary wire, a charging station loop and the chargingstation and wherein the boundary wire makes a loop in the chargingstation that is narrower than and crosses the charging station loop, therobotic mower further comprising a control unit and at least one sensor,wherein the control unit comprises a processor and a memory, the memorycomprising instructions which when executed by the processer causes thesystem to: receive a return signal from the control unit that therobotic mower shall return to the charging station, control the roboticmower to follow the boundary wire at a distance, detect the chargingstation loop by means of the at least one sensor, control the roboticmower to follow the charging station loop, in a direction away from theboundary wire, with at least one sensor, detect, by means of the atleast one sensor, a crossing between the charging station loop and theboundary wire loop, control the robotic mower to follow the chargingstation loop a first distance after detection of the crossing, continueto drive the robotic mower in a direction straight forward for a seconddistance, turn, by means of the control unit, the robotic mower towardsthe charging station, and control the robotic mower to follow theboundary wire loop with at least one sensor until a charging position isreached.
 30. The system according to claim 29, which is further causedto follow the boundary wire at a random distance.
 31. The systemaccording to claim 29, which is further caused to determine that thefirst distance and the second distance are reached when at least onesensor is in a known position in front of the charging station.
 32. Thesystem according to claim 29, which is further caused to determine thatthe first distance and the second distance are predetermined distances.33. The system according to claim 29, which is further caused to turnthe robotic mower towards the charging station until at least one sensorpasses the boundary wire loop.
 34. The system according to claim 29,wherein the robotic mower is provided with three sensors, two frontsensors and one rear sensor and wherein the system is further caused todetermine detection of the charging station loop when one of the frontsensors passes the charging station loop.
 35. The system according toclaim 29, wherein the robotic mower is provided with two front sensorsand two rear sensors and wherein the first distance and the seconddistance are reached when one of the two rear sensors reaches thecharging station loop and the boundary wire loop, respectively.
 36. Amethod performed by a system for docketing a robotic mower with acharging station, the system comprising the robotic mower having acontrol unit and at least one sensor, a boundary wire, a chargingstation loop, the charging station and at least one guide wire andwherein the boundary wire makes a loop in the charging station that isnarrower than and crosses the charging station loop, the methodcomprising: receiving a return signal from the control unit that therobotic mower shall return to the charging station, controlling therobotic mower to follow the guide wire at a random distance, detectingthe charging station loop by means of the at least one sensor,controlling the robotic mower to move closer to the guide wire,detecting, by means of the at least one sensor, that the robotic mowerpasses the boundary wire loop, and controlling the robotic mower tofollow the boundary wire loop with at least one sensor until a chargingposition is reached.
 37. The method according to claim 36, wherein therobotic mower is provided with two front sensors and one rear sensor andwherein the detection of the boundary wire loop is determined when oneof the front sensors passes the charging station loop.
 38. The methodaccording to any of claim 36, wherein both front sensors are used tocontrol the robotic mower, such that the robotic mower follows theboundary wire loop to the charging position.
 39. A system for docketinga robotic mower with a charging station, comprising the robotic mower, aboundary wire, at least one guide wire, a charging station loop and thecharging station and wherein the boundary wire makes a loop in thecharging station that is narrower than and crosses the charging stationloop, the robotic mower further comprising a control unit and at leastone sensor, wherein the control unit comprises a processor and a memory,the memory comprising instructions which when executed by the processercauses the system to: receive a return signal from the control unit thatthe robotic mower shall return to the charging station, control therobotic mower to follow the guide wire at a random distance, detect thecharging station loop by means of the at least one sensor, control therobotic mower to move closer to the guide wire, detect, by means of theat least one sensor, that the robotic mower passes the boundary wireloop, and control the robotic mower to follow the boundary wire loopwith at least one sensor until a charging position is reached.
 40. Thesystem according to claim 39, wherein the robotic mower is provided withtwo front sensors and one rear sensor and wherein the system is furthercaused to determine detection of the charging station loop when one ofthe front sensors passes the charging station loop.
 41. The systemaccording to claim 39, which is further caused to use both front sensorsto control the robotic mower, such that the robotic mower follows theboundary wire loop to the charging position.
 42. A computer programcomprising computer program code, the computer program code beingadapted, if executed by the processers of the control unit, to implementthe method according to claim
 22. 43. A computer program comprisingcomputer program code, the computer program code being adapted, ifexecuted by the processers of the control unit, to implement the methodaccording to claim 36.